/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.hdfs.server.datanode.metrics;
import java.util.Random;

import javax.management.ObjectName;
import org.apache.hadoop.metrics.util.MBeanUtil;
import org.apache.hadoop.metrics.util.MetricsDynamicMBeanBase;
import org.apache.hadoop.metrics.util.MetricsRegistry;

/**
 * 
 * This is the JMX MBean for reporting the DataNode Activity.
 * The MBean is register using the name
 *        "hadoop:service=DataNode,name=DataNodeActivity-<storageid>"
 * 
 * Many of the activity metrics are sampled and averaged on an interval 
 * which can be specified in the metrics config file.
 * <p>
 * For the metrics that are sampled and averaged, one must specify 
 * a metrics context that does periodic update calls. Most metrics contexts do.
 * The default Null metrics context however does NOT. So if you aren't
 * using any other metrics context then you can turn on the viewing and averaging
 * of sampled metrics by  specifying the following two lines
 *  in the hadoop-meterics.properties file:
*  <pre>
 *        dfs.class=org.apache.hadoop.metrics.spi.NullContextWithUpdateThread
 *        dfs.period=10
 *  </pre>
 *<p>
 * Note that the metrics are collected regardless of the context used.
 * The context with the update thread is used to average the data periodically
 *
 *
 *
 * Impl details: We use a dynamic mbean that gets the list of the metrics
 * from the metrics registry passed as an argument to the constructor
 */

public class DataNodeActivityMBean extends MetricsDynamicMBeanBase {
  final private ObjectName mbeanName;
  private Random rand = new Random(); 

  public DataNodeActivityMBean(final MetricsRegistry mr, final String storageId) {
    super(mr, "Activity statistics at the DataNode");
    String storageName;
    if (storageId.equals("")) {// Temp fix for the uninitialized storage
      storageName = "UndefinedStorageId" + rand.nextInt();
    } else {
      storageName = storageId;
    }
    mbeanName = MBeanUtil.registerMBean("DataNode", "DataNodeActivity-" + storageName, this);
  }
  

  public void shutdown() {
    if (mbeanName != null)
      MBeanUtil.unregisterMBean(mbeanName);
  }
}
